1996 HDJ 80 (445,000 kms) Sometimes stumbling/stalling on pullaway.

[Snatchblock]

Hi Gents, can anyone help with this? I bought the truck last year, and have used it mainly for back country skiing, with no problems.

I drove my 1996 HDJ 80 to the uk last month from Norway, no issues, (about 2000 km) other than if really giving it the beans there was a slight stumble.. It sits at 100kph at 2200 rpm. As my daughter, was going to be driving it home I thought that I might change the fuel filter. It ended up being done at the Toyota stealership. On the way home from the uk she told me that occasionally on start up, it revs up to 1200 rpm, and stays there for 4/500 m. Then accelerates and drives as normal.

Then my wife borrowed it, and after struggling for 400m it stopped and would not restart. Once the filter was pumped full again, it ran smoothly.

I suspected a problem before the filter, so pulled the filter out of the tank, both the tank and filter were clean. Car runs fine when I drive it. It is obviously a long standing issue, because a previous owner has installed one of those bulbs that you squeeze to pull fuel from the tank into the fuel line. The priming handle on the fuel filter works, once pumped hard, it gradually looses pressure. If/when the engine stalls, there is no pressure in the fuel filter, once pumped up, it restarts first hit. It can also start first hit without pumping the fuel filter. The fuel pump idle screw would appear to have been set a little low, and this fact covered by applying a little tension on the hand throttle. Any smart ideas?

 

[mudgudgeon]

I thought that I might change the fuel filter.

Almost guaranteed this is the cause of your stumble.

A few related possible causes -

- the new filter wasn't screwed on tight enough,
- or an oring is compromised,
- or the diaphragm in the hand primer pump/ fuel filter assembly has failed
- or an old, hard rubber fuel hose was removed and reused. They rarely reseal effectively.

What is happening?
You are getting air sucked into the fuel lines. Its common with diesels that have a suction pump in the injection pump ( 1hd-t). Fuel lines are under vacuum so a cracked hose, a leaky oring or diaphragm can allow air to be sucked in without any visible fuel leak.
Air in fuel lines gets compressed by the injection pump, then expands in the injection line before fuel gets to the injector. Then there's not enough pressure to force the injector to "pop" open, you get no fuel injected into a cylinder on that cycle or fuel gets injected late in the cycle.

The result is a stumble, most noticeable at lower RPM when accelerating. Late injection effectively retards the timing.
You'll get poorly burnt, or unburnt diesel in the exhaust. You might see this as white smoke from the exhaust, and exhaust fumes that stink strongly of raw diesel.
You might also find cold starts difficult after the vehicle has sat for a little while.

You can verify if you have air getting in the fuel system by temporarily installing a piece of clear pvc hose between the filter assembly and the injection pump. If you see bubbles with the engine running, you have a leak in the fuel system.

Loads of threads talking about this in the diesel tech forum here

 

[mudgudgeon]

In regards to idle, fix the air leak first.

If the idle issue is still present, you can increase idle speed with the idle speed screw on the injector pump lever arm where the throttle linkage connects to the pump.
Just be sure you keep the smallest amount of slack in the throttle cable and throttle linkage adjustment. You want minimal slack in the linkages, but not excess slack, and also don't want it all under tension at idle either.

 

[Snatchblock]

Almost guaranteed this is the cause of your stumble.

A few related possible causes -

- the new filter wasn't screwed on tight enough,
- or an oring is compromised,
- or the diaphragm in the hand primer pump/ fuel filter assembly has failed
- or an old, hard rubber fuel hose was removed and reused. They rarely reseal effectively.

What is happening?
You are getting air sucked into the fuel lines. Its common with diesels that have a suction pump in the injection pump ( 1hd-t). Fuel lines are under vacuum so a cracked hose, a leaky oring or diaphragm can allow air to be sucked in without any visible fuel leak.
Air in fuel lines gets compressed by the injection pump, then expands in the injection line before fuel gets to the injector. Then there's not enough pressure to force the injector to "pop" open, you get no fuel injected into a cylinder on that cycle or fuel gets injected late in the cycle.

The result is a stumble, most noticeable at lower RPM when accelerating. Late injection effectively retards the timing.
You'll get poorly burnt, or unburnt diesel in the exhaust. You might see this as white smoke from the exhaust, and exhaust fumes that stink strongly of raw diesel.
You might also find cold starts difficult after the vehicle has sat for a little while.

You can verify if you have air getting in the fuel system by temporarily installing a piece of clear pvc hose between the filter assembly and the injection pump. If you see bubbles with the engine running, you have a leak in the fuel system.

Loads of threads talking about this in the diesel tech forum here

Many thanks, will investigate!

 

[Snatchblock]

Quick update. I found a small leak in the soft hose leading to the filter mounting. So i have replaced that, and so far that seems to have fixed the issue. Many thanks to all for the suggestions!